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Old 11-02-2015, 21:59   #1
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Setting up solar array

I am installing 4 x 180 watt panels on a frame at the back of our cat and are looking for a few answers regarding wiring sizes and sizing the charge controller.

As I don't want shading to be an issue so I would like to install them in Parallel. I am looking at using 4 to 1 MC4 branches (splitters) to connect to panels and parallel them into a junction box from which I will run two 4 awg wires 25ft to an 80 amp Outback charge controller and then another 5 ft to the battery bank.

Does this sound reasonable?
Could I get away with using a smaller wire size 6 awg or so?
How do I work out how much amperage will be flowing in this parallel set up? I want to make sure the splitters can carry the amps.
If I wanted to add more panels down the road how much room (in wattage) do I have left on the charge controller?

Would appreciate any feedback


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Old 12-02-2015, 02:55   #2
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Re: Setting up solar array

You didnt mention the voltage of the panels or whether the Outback is an mppt controller?

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Old 12-02-2015, 05:26   #3
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Re: Setting up solar array

The panels are 24V and the Outback is an MPPT controller.


Here are the panel specs:

Rated power (Pmax)1 180W
Power tolerance 3%
Module efficiency 14.10%
Maximum power voltage (Vmpp) 36.00V
Maximum power current (Impp) 5.00A
Open circuit voltage (Voc) 45.0V
Short circuit current (Isc) 5.2A
Nominal Operating Cell
Temperature (NOCT) 45.9C/114.6F
Temperature coefficient (Pmax) -0.44%/C
Temperature coefficient (Voc) -0.33%/C
Temperature coeficient (Isc) +0.03%/C
Operating temperature range -40C - +85C /
-40F - +136F
Maximum system voltage 600V (UL) /1000V (IEC)
Maximum Series Fuse Rating 10A
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Old 12-02-2015, 18:06   #4
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Re: Setting up solar array

This is sort of a WAG here, but if you're interested in knowing exactly how big of a controller to get (as you were asking in regard to panel expansion down the road), couldn't you just add together all the "MAXIMUM series fuse ratings" of each panel to determine a conservative MINIMUM size controller? In your case, each panel is rated 10A for max fuse protection. 10A x 4 panels = 40A min size controller? Is your 80A controller 80 amps 12v, 40A 24v? or is it 80A 24v? Or am I asking the wrong question.... I am learning too here.
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Old 13-02-2015, 08:27   #5
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Re: Setting up solar array

Thx for your reply, I am not sure but I don't think the sum of the max amperage is the way to work out the remaining amps on the charge controller. Factors like running the panels in parallel or series, 12 or 24v will affect the calculation. I was hoping that some of the solar gurus on the CF might be able to shed some light on working this out.

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Old 13-02-2015, 15:39   #6
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Re: Setting up solar array

The controller is rated for its amp output.

An MPPT controller will take the 10A X 4 panels = 40 amp @ 24 volts, and make 80 amps @ 12 volt output.

He could also run the panels in series. 24 volt X 4= 96 volts @10 amps, and the controller will convert that to 80 amps at 12 volt output. With that setup, you could use much lighter wire, but shade on 1 panel, will stop any output.

All numbers are only for example.

Hope this helped

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Old 13-02-2015, 17:13   #7
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Re: Setting up solar array

I would definitely wire them in series. I think you will find it's actually more immune to shading. I've got the same controller with 3 250W panels.
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Old 13-02-2015, 20:06   #8
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Re: Setting up solar array

So far you've gotten some good advice.

I don't call solar panels "12v" or "24v" etc, your panels are 36v panels and the most important number is your 45Voc. This will determine the max. number of panels in series based on max. input voltage of your controller.

Your controller is rated at 150v input max. So with those panels, you would be able to connect them in 2 parallel strings of 2 ea. If you had 6, you could do 2 strings of 3 ea with a max voltage of 135v.

As far as max. wattage goes, *theoretically* you could put 1250w on it for a 12V battery bank, or if you have a 24v battery bank, you could install 2500w.

However, since MPPT controllers self regulate to their max. output, there isn't anything wrong with going big if you have the room for it. The 1250watts = 80 amps equation would be under perfect conditions - midsummer, noon, no shading, etc. The reality is, the panels are mounted flat, the sun is rarely directly overhead, the winter sun is lower in the sky and there is always shading on a boat. So if you have the room for it, you could install 8 panels for 1440 watts and you'd get more power, more often, for longer periods without blowing anything up.

As far as wire size goes, the higher the voltage, the lower the current, which allows you to get away with a smaller gauge wire. The correct answer would be based on total length from panels to controller (both ways, not one way) and total current expected when you've finished adding panels. I'd strongly recommend a 2 panels per string setup unless you decide to install panels in sets of 3, in which case you could install 3 panels strings for a max of 6 or 9. If you plan on doing 8 panels then figure 4 strings of 2 panels in series. The 90Voc and 20 amp current max. at the junction box would dictate your correct wire size from there to the controller. The short branch connections to the junction box with 10awg and MC4 connectors should be fine, if all 8 panels are next to each other. If you have them spread out all over the boat, then you'll have to calculate branch wire size based on 5A per branch.

Hope this helps!

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